Process for the manufacture of iron oxide



Patented July 7, 1942 Thomas Glenwright French, Newcastle-on-Tyne, England, assignor to The Priestman Collieries Limited, Newcastle-on-Tyne, England, a British company No Drawing. Application October 16, 1939, Serial No. 299,761. In Great Britain September 30,

3 Claims. (01. 23-200) This invention relates to processes for the manufacture of iron oxide of the kind comprising precipitating a ferrous hydroxide by the electrolysis with iron electrodes of a solution of ionizable alkaline metal salts such as sodium and/or potassium salt.

The object of the invention is to provide a process for the manufacture of iron oxide for use mainly as a black, brown or red pigment of According to one process an electrolyte of 'sodium chloride or sodium sulphate of density sp. gr. 1.10 is introduced into wood vats, into which are placed iron or mild steel anodes connected to a supply of D. C. current.

The electrolyte is maintained at a temperature of 80 to 90 C., and the current density is approximately .3 amp. per square inch.

The electrolysis produces a bluish white premaximum purity, and which will be cheaper to cipitate of ferrous hydroxide of an extremely carry into effect than has been the case hitherto. tenuous nature. Owing to the exposure of the Heretofore proposals have been made for the electrolyte to the atmosphere, this precipitate in production of iron oxide for the manufacture of time would become oxidised to a black ferricpigments which have consisted in precipitating ferrous hydroxide. However to accelerate the a ferrous oxide by the chemical process of addprocess of oxidation, air is continuously blown ing hydrate of lime, carbonate of soda or the into the electrolyte. The continuous blowing of equivalent, to a solution of a ferrous salt such air into the electrolyte also results in a precipias ferrous sulphate, and oxidising the precipitate which settles easily and more readily'sepatated ferrous oxide by blowing air into the solurates from the electrolyte by filtration in a filter tion containing the precipitate to convert the press. The black hydroxide is washed with water ferrous to ferric oxide. In another proposal, the in a filter press, dried in a hot air oven at 100 ferrous oxide was precipitated electrolytically, C., and subsequently ground to the requisite fineremoved from the electrolytic bath, washed and ness in a suitable mill. dried, and then roasted to produce ferric oxide. The product after drying is a black hydroxide According to another electrolytic process, the of iron, stable at 100 C. solutions produced at the respective electrodes To produce th r 0 101115 of oxid from brown were each led away in separate streams and subt deep r d, the black hydroxide is calcined in q n y brought together Outside the electrolya suitable furnace with excess air, the degree of sis cell to precipitate the ferrous oxide which temperature affecting the resulting colour. For was Subsequently oxidised mother liquor. example at 2Q0 C. a brown is obtained I have found that by Producing the iron oxide at 600 0. a bright Turkey red is obtained, at electrolytically, a finer quality of pigment is ob- 00 a, deep Turkey red and at 10000 an tained than with chemical methods, and accorddian red pigment is produced. ing to the present invention the electrolytic me In drder to produce a maroon or ochre like eipiieiion 9 the 'PP hydroxlde 1S cqmbmed pigment, in an alternative process the paste from the -o of the made the filter press is mixed with water to form a ciplta'Ped Whlle Stm m suspanslol} m the 6180' slurry. To the slurry is added an oxidizing agent, trolytic bath to produce a ferric-ferrous hypreferably a solution of sodium hypocmorite dmxide' m f t 4 which oxidizing agent is preferably made by In.add1t1n to the Q 0 plgmen 0 electrolysis of sodium chloride. The whole mixobtamed by electrolytic precipitation of the iron ture is then boiled until a ferric hydroxide of oxide as above mentioned, the process according niform 1i ht brown c010 is btained F to the invention reduces the number of reagents :ulnh o epmus ate is then added and the boiling continued employed to a minimum, and, with the oonvenm f h d hr t k ience'of cheap electric power for the electrolytic 1 3 ,5 g e plgmen nown as precipitation, enables the complete process to be em 8 OW 1s orme carried out in one industrial-as distinct from The Plgment separated y means Of a filter chemicaloperation, and so gives an improved g g: Ki ali wlth water and the Paste dned n 1 nt by means of a cheap and co Ven e If desired air may lie blown through in addi- In order t obtain maximmn purity the l tion the step of adding the oxidizing agent. trolysis current is preferably reversed at inter- It 15 Important that the oxidizing ent be vals of about 30 minutes. Otherwise there is a introduced apart m t e ct o te. tendency for metallic iron coming down as black By calcining with excess of air as mentioned specks in connection with the first process a similar range of shades from light maroon or ochre to dark maroon may be obtained.

According to one example of the above alternative process, an electrolysis vat containing sodium chloride is connected in closed circuit with the mixing vat. Sodium hypochlorite from the electrolysis vat is admitted to the mixing vat and at the same time the mixture in the mixing vat is subjected to boiling. Sodium hypochlorite is continued to be admitted to the mixing vat until the required amount of oxidation has taken place as a result of the combined action of the 7 liquor in the mixing vat--which is sodium chloride,is pumped back to the electrolysis vat.

Ferric sulphate is now added to the paste in the mixing vat and boiling is continued until the ferric hydroxide ochre or ferrite pigment is obtained.

The pigment is then transferred to a second filter press, separated and washed anddried, and if desired calcined to temperatures depending on the depth of colour required.

By the process according to the invention iron oxide pigment from black to deep reds, maroons or ochres of a purity of 99.5% is obtained.

I claim:

1. The process for producing maroon or ochre like pigments, comprising precipitating ferrous hydroxide by the electrolysis with iron electrodes of a solution of an ionizable alkali metal salt, and oxidising the ferrous hydroxide precipitated while in suspension in the electrolysis bath to produce a ferric ferrous hydroxide, washing with water the ferric ferrous hydroxide, separating the said hydroxide, mixing the hydroxide. with water to form a slurry, adding an oxidising agent to said slurry, boiling the mixture until a ferric hydroxide of uniform light brown colour is obtained, then adding ferrous sulphate and continuing boiling until a ferric hydroxide ochre pigment known as ferrite is obtained.

2. The process for producing maroon or ochre like pigments, comprising precipitating ferrous hydroxide by the electrolysis with iron electrodes of a solution of an ionizable alkali metal salt, and oxidising the ferrous hydroxide precipitated while in suspension in the electrolysis bath to produce a ferric ferrous hydroxide, washing with water the ferric ferrous hydroxide, separating the said hydroxide, mixing the hydroxide with water to form a slurry.'adding sodium hypochlorite to said slurry, boiling the mixture until a uniform light brown colour is obtained, then adding ferrous sulphate and continuing boiling until a ferric hydroxide ochre pigment known as ferrite is obtained.

3. The process for producing maroon or ochre like pigments, comprising precipitating ferrous hydroxide by the electrolysis with iron electrodes of a solution of an ionizable alkali metal salt, and oxidising the ferrous hydroxide precipitated while in suspension in the electrolysis bath to produce a ferric ferrous hydroxide, washing with water the ferric ferrous hydroxide, separating the said hydroxide, mixing the hydroxide with water to form a slurry, adding to said slurry sodium hypochlorite which is obtained by the electrolysis of sodium chloride, the sodium hypochlorite giving up its oxygen during the first boiling and the resulting restored sodium chloride being used again in the electrolysis process for producing the sodium hypochlorite, the same sodium chloride thus being usable continually as an oxygen carrier for the oxidation step, boiling the mixture until a uniform light brown colour is obtained, then adding ferrous sulphate and continuing boiling until a ferric hydroxide ochre pigment known as ferrite is obtained.

THOMAS GLENWRIGHT FRENCH. 

